The odontolite is lighter than the mineral turquois, changes color by artificial light, loses color in distilled water and alcohol, and is translucent on the edges.
This fossil turquois does not fade like the mineral turquois, but by artificial light appears of a dirty grayish-blue.
Turquoises are sometimes artificially stained, but this can be detected by applying a drop of ammonia to the back of the stone, and if the color is artificial the ammonia will eat it off, leaving a green spot. Ammonia does not affect the color of the Persian turquois. The so-called “reconstructed” turquoises are very close imitations of the real, but are easily distinguished, as they change rapidly to a deeper blue when immersed in water, and while wet the surface of the stone shows cracks in every direction. These stones become softer through soaking in water or alcohol. The original color, however, returns when the stone is dry, but the cracks remain in faint outline.
Tourmaline.
The tourmaline or precious schorl is known under many different names, and no other mineral has such a suite of colors.
The colorless variety is known as achroite; the red, as rubellite or siberite; the blue, indicolite or Brazilian sapphire; the green, Brazilian emerald; and the yellowish-green, Ceylon chrysolite or Ceylon peridot. Besides the above colors and their shadings, the tourmaline occurs in black and brown.
The crystallization is obtuse rhomboid, and generally forms six-, nine-, and twelve-sided prisms.
Some of the crystals are very large, specimens over eight inches long having been mined.
The tourmaline crystals are remarkable for their varied and beautiful groupings of colors. Some are internally blue or brown, surrounded by a bright carmine red or dull yellow; others are red internally and are enveloped by a green exterior; crystals are sometimes pink at the summit and light green at the base, or crimson tipped with black, or white at one end shading into green and finally into red at the other end. The hardness of the tourmaline is 7 to 7.5, specific gravity 3 to 3.1, and lustre vitreous.
The tourmaline becomes decidedly electric by heating or rubbing, and will readily attract small pieces of paper and other small objects. The rubellite or red tourmaline is composed of: